Method of inhibiting corrosion of copper and cuprous alloys in contact with water



Un t s George B. Hatch, Allison Park, Pa., assignor to Hagan Chemicals '8: Controls, Inc., a corporation of Pennsylvania .No Drawing. FiIed JuIy 27, 1956, Ser. No. 600,369

10 Claims. or. 252-389) This invention relates in general to the over-all inhibition of corrosion in systems where copper or its alloys are present together with more anodic metals such as iron, zinc, and aluminum or their alloys.

It relates in particular to (a) a method of rapidly reducing the galvanic attack of steel coupled to cuprous metals, (b) the reduction or elimination of the dissolving of copper by water in passing through portions of a water system which are made from cuprous materials, the reduction or elimination of the deleterious action of dissolved copper on the corrosion of more anodicmetals such assteel, zinc and aluminum in a water system and (d) the reduction or elimination of the deleterious action of mercury salts in the corrosion of copper.

In US. Patent 2,337,856 of which I am co-patentee, the'method of preventing corrosion of ferrous metals by the addition of small amounts of molecularly dehydrated ess are the thiols of compounds selected from the'fgroup consisting of thiazoles, oXazoles, and imidazoles.

'I have discovered that the hetero'cyclic fcompounds. known as 1,2,3-triazoles having the general configuration known as 1,2,3 -be n,zotr iaiole),- having the structural formula possess certain features'which make them extremely useful in controlling corrosion of copper, both in the presence of the molecularly dehydrated phosphates or in their absence. These compounds are of particular advantage in treating recirculating water, where addition of certain chlorinated compounds is required to control algae and other objectionable growths.

Although the direct addition of chlorine per se will destroy any protective film of benzotriazole on copper, if a chloramine is employed as a source of chlorine, the benzotriazole is not affected, but on the contrary, chloramine will oxidize mercaptobenzothiazole or other thiazoles rendering them completely ineflective for protect- 2,941,953 Patented June 21, 1960 ice 2 ing copper or copper alloys. Chloramine-T is a well known source of chlorine having the formula and it, as well as other chloramines, areused for algae particularly where mercury is to be recovered from the cooling water eflluent for subsequent con-version to inercury itself. I 1

To determine the effect of benzotriazole as a' copper corrosion inhibitor, I prepared a number of copper strips 1 /2 inch x 1 /2 inch which were immersed in beakers of Pittsburgh city tap water adjusted to pH 5.5 with hydrochloric acid. These were agitated for five days at degrees centigrade. In Table 1 is shown the influence of benzotriazole concentrations on the weight loss of the copper and on the amounts of copper picked up by the water. In this series of tests 25 parts per million of Calgon brand sodium phosphate glass, a commonly used molecularly dehydrated phosphate, were present in solut1on. I

Table 1 Copper weight Copper loss in pickup by V Beuzotrlazole (Parts per million) milligrams water in per square parts per decimeter million per day .7 7450' particularly thecompound benzotriazole- (sometimes below in Table 3.

In Table 2 below I have reported data from tests using 2 parts per million ofbenzotriazole at solution pH values ranging from 2 through 7. Here again I added25 parts per million of Calgon brand sodium phosphate glass which has a molar ratio of sodium oxide to phosphorus pentoxide of 1.1:1 as well as 2 parts per million of the benzotriazole. 7

Table 2 Weight loss Pickup of of copper copper in pH Values milligrams .in water per square in parts decimeter per per day million The foregoing data illustrates the eifect of pH on the performance of the benzotriazole, the compound being most effective in the range of 5-7.

To illustrate the effect of chlorine and chloramine-T on the protective effect of benzotriazole on copper, I ran a series of tests similar in all respects as to time and .temperature, at a pH value of.5 .5, adding chlorine in the form of sodium hypochlorite .(in an amount equivalent-to 2 parts per million of chlorine), one-half hour after starting the beaker'tests, and chloramine-T (in an amount equivalent to 2 parts per million of chlorine)'one-half hour after starting the tests. This data issummarized With regard to the inhibition of the deleterious action of dissolved mercury on copper, I prepared a series of.

copper strips 1% inch. These were'immersed in Pittsburgh city tap water at a pH of 5.5 and a concentration of 2 parts. per million of benzotriazole and 25 parts per galvanic attack of steel coupled to copper when the henzotriazole is used in conjunction with molecularly dehydrated phosphates was established by certain procedures hereinafter to be disclosed.

To illustrate the effectiveness .of benzotriazole in the inhibition of the galvanic attack of steel coupled to copper, a test procedure described in Industrial and Engineering Chemistry, vol. 44, page 1781 (1952), was followed. The salient features of this method are as follows:

The test strips were 1 /2 x 1 /2-inch metal plates. The steel test panels were cold-rolled low carbon strips. Pittsburgh tap water adjusted to the desired pH with HCl served as the test medium. The analysis of the water used in the tests is sh'own'in Table l. Agitation was provided million ofphesphete in the form of e Sodium-Zine P by lateral movement of the plates back and forth over a phate glass having the molar composition distance of two inches through one liter portions of water at a rate of 32 cyles/minute. The tests were conducted 1'12Na 2O'029.ZnO'P2( )5 at 35 C102. The metal plates were cleaned to a zero was malmamed. In this expenmem (ldentlfied as Senes waterbreak in' an alkaline cleaner prior to use. Copper A below) the concentratlon of mercurY (added m the test panels were pickled by a 10 percent nitric acid dip form of a water soluble mercury slat this'instance after the alkaline cleaning. At the conclusion of the mercuric ehlolide) ed f om to 0.5 part per mill tests where weight loss data were collected, the steel the Weight loss of copper mdlcaPing the del'stenous panels were pickled in 36 percent hydrochloric acid inaetlon 'e Y on the QPP Strips, Well the hibited with 5 percent stannous chloride and 2 percent copper P P Parts Per PB ffmnd s antimony oxide; the copper panels were pickled in 5 perwater, are mdloated: the con'fpanson belng each cent sulfuric acid.. Pickling blanks were determined and stance between water to which 'benzotnazole and the observed weight losses corrected accordingly. Ph p We added on the one hand and the same Pittsburgh tap water was used as the corrosive medium Water p p ph p alone with the pH adjusted to 5.5 with hydrochloric acid.

A similar expellment l' B below) was conducted The following data appearing in Table 6 was obtained: using Calgon brand phosphate instead of the zinc-containing phosphate; and data from both tests is shown below. Table 6 T bl 4 A. CONTROL (UNTREATED TAP WATER pH 5.5

Time in Hours Current in Mercury Wt. loss of Copper Milliamperes in Solution copper in pickup in Parts per mg./dm. parts per million day million 0... 0 ,6 1.57 1 1. 02 0 0. 0- 0. 01 2..- 1. 63

ti o as as 1:91 0.5 0.07 0.10 p 0 0.28 0. 04 series}; B. TAP WATER +5 P.P.M. BENZOTRIAZOLE H 5.5)

Weight losses ranged from 2.5-5.0 mg./drn. /day in 8%; the case of water to which no benzotriazole Was added 4 and the copper pickup ranged from 0.74 to 2.47 parts i e33 per million. In making these comparisons the phosphates in a 25 parts ct million concentration Were added to the TAP WATER +50 g% ioN R D PHOSPHATE water.

Prevention of the deposition of copper on aluminum 0 0 which has heretofore been indicated as one of the benefits t. 4 conferred by using benzotriazole is shown inthe table be- 3-21 low where Pittsburgh city tap water containing 0.5 part 4"' 0: 26 per million of copper (added in the form of cupric sulfate), the Water being maintained at a pH of 5.5; was prepared. Strips of 3004-Hl4 aluminum were immersed TAP WATER +50 z' gig h i' BENZOTRIA- with agition at 35 degrees centigr'ade for .five' days in 1 this water, the benzotriazole concentration in parts per n 0 million ranging from 0 to 10. The Weight loss in milli- 0.13 grams per square decimeter per day of aluminum is shown gggg in Table 5. 4 0. 04s 1 Table 5 0. 045

weightloss of The foregoing data forcefully demonstrates that there Concentration of Benzotriazole in parts per million aluminum in is Synerglstlc coactlon between the P l P p -l fil y (molecularly dehydrated phosphate) and the benzotriazole to inhibit galvanic action with extreme rapidity. At 8- 3 the end of 5 hours, for example, the current in the 1 3 water treated with phosphate-benzotriazole is only 0.045 g-g- 3-3; milliampere as compared with 0.33 in the water treated 10.0 1:30 with benzotriazole alone, 0.22 in the water treated with phosphate alone and 1.71 in the control. Observation of The effectiveness of benzotriazole for inhibiting the 7 the data shown in B and C above would not indicate in any way the extremely low values which might be obtained when B and C are combined in D.

I have found that benzotriazole is soluble in water under the conditions of use which I comtemplate to the extent of about 1.4%. Although any amount of benzotriazole up to the limit of its solubility can be used for my purposes, surprisingly small amounts are quite efiective, as little as 0.05 part per million showing an inhibitory effect. Practically, I prefer to use from 0.5 part per million to about 5 parts per million for the various corrosion inhibiting uses which I have herein outlined.

Although I have used specific concentrations of certain polyphosphates in some of the examples set forth herein, the range of concentrations and the particular phosphates which may be used will generally follow the applicable part of the teachings outlined in U.S. Patent 2,742,369 hereinbefore mentioned, a detailed discussion appearing in columns 5 and 6 thereof U.S. Patent 2,742,369 contains, as a part of its disclosure, the entire disclosure of U.S. Patent 2,337,856, hereinbefore mentioned. These two patents abundantly establish that very small amounts of molecularly dehydrated phosphates, indeed as little as 0.1 ppm, are sufiicient to form a protective film on metals. The present invention deals with the eflicacy of benzotriazole as a copper corrosion inhibitor, used in some applications with polyphosphates and in others demonstrating its elfectiveness without the addition of the phosphates. As a practical matter where iron or steel are present in a-Water system, I must inhibit their corrosion, preferably by using one of the above mentioned phosphates in the manner of U.S. Patent 2,337,856 and U.S. Patent 2,742,369, if the benzotriazole is to function elfectively as a copper inhibitor.

Although I have demonstrated the unusual effects of the 1,2,3-triazoles with 1,2,3-benzotriazole, I may use any water-soluble 1,2,3-triazoles such as 1,2,3 triazole itself or a substituted 1,2,3-triazole Where the substitution takes place in either the 4 or 5 position (or both) of the triazole ring as shown here by the structural formula I claim:

1. The method of retarding the corrosion of copper and cuprous alloys in contact with water under conditions where said water is also in contact with ferrous metals which comprises adding to the water from about 2. The method as described in claim 1 where the 1,2,3 -triazole is 1,2,3-benzotriazole, and the alkali-metal polyphosphate has a molar ratio of alkali-metal oxide to phosphorous pentoxide of from about 0.9 to 1 to about 2 to 1.

3. A method of protecting copper and copper alloys in contact with aqueous media against corrosion in the presence of chloramine which comprises maintaining in the aqueous media a concentration of from about 0.05 part to about 5.0 parts of a water-soluble l,2,3 triazole.

4. The method as described in claim 3 where the 1,2,3- triazole is 1,2,3-benzotriazole.

5. A method of protecting copper and cuprous metals in a system for transporting aqueous media against corrosion in the presence of ferrous metals where chloramine is also present in the system, which comprises maintaining in the system from about 0.05 part to about 5.0 parts per million of a 1,2,3-triazole and a water-soluble alkali-metal polyphosphate the latter being present in a concentration not exceeding 50 parts per million.

6. The method as described in claim 5 where the 1,2,3-

triazole is 1,2,3-benzotriazole.

7. A method of reducing the corrosion of copper by dissolved mercury salts in a water system which comprises maintaining in said system from about 0.05 part to about 5.0 parts of a water soluble 1,2,3-triazole per million parts of water.

8. The method as described in claim 7 where the triazole is 1,2,3-benzotriazole in an amount which is from about 0.5 part to about 5.0 parts per million parts of water in said system.

9. A method of inhibiting the deleterious action of dissolved copper in aqueous media on ferrous metals and aluminum and its alloys by maintaining in solution in said aqueous media from about 0.05 part to about 5.0 parts of a 1,2,3-triazole per million parts of water.

10. The method as described in claim 9 where the 1,2,3-triazole is 1,2,3-benzotriazole.

References Cited in the file of this patent UNITED STATES PATENTS 2,337,856 Rice et al Dec. 28, 1943 2,618,606 Schaefier Nov. 18, 1952 2,803,603 Meighen Aug. 20, 1957 

1. THE METHOD OF RETARDING THE CORRISION OF COPPER AND CUPROUS ALLYS IN CONTACT WITH WATER UNDER CONDITIONS WHERE SAID WATER IS ALSO IN CONTACT WITH FERROUS METALS WHICH COMPRISES ADDING TO THE WATER FROM ABOUT 0.05 TO ABOUT 5.0 PARTS OF A WATER-SOLUBLE 1,2,3-TRIAZOLE PER MILLION PARTS OF WATER AND A WATER-SOLUBLE ALKALI-METAL POLYPHOSPHATE IN AN AMOUNT SUFFICIENT TO FORM A PROTECTIVE FILM, BUT NOT EXCEEDING 50 PARTS PER MILLION PARTS OF WATER
 3. A METHOD OF PROTECTING COPPER AND COPPER ALLOYS IN CONTACT WITH AQUEOUS MEDIA AGAINST CORROSION IN THE PRESENCE OF CHLORAMINE WHICH COMPRISES MAINTAINING IN THE AQUEOUS MEDIA A CONCENTRATION OF FROM ABOUT 0.05 PART TO ABOUT 5.0 PARTS OF A WATER-SOLUBLE 1,2,3-TRIAZOLE. 